Production of annealed tubing by strand annealing process



J. HERREN ETAL 3,518,405

June 30, 1970 PRODUCTION OF ANNEALED TUBING BY STRAND ANNEALIN" PROCESS Filed Feb. 19, 1968 T fi 62- FIGI INVENTORS JAMES L. HERREN EDWARD P. HA8 A5 United States Patent 3,518,405 PRODUCTION OF ANNEALED TUBING BY STRAND ANNEALING PROCESS James L. Herren, Decatur, Ala., and Edward P. Habdas,

Dearborn, Mich., assignors to Calumet & Hecla Corporation, Allen Park, Mich., a corporation of Delaware Filed Feb. 19, 1968, Ser. No. 706,589

Int. Cl. C21d 9/6'2 US. Cl. 219155 3 Claims ABSTRACT OF THE DISCLOSURE Metal tubing such as thin-walled copper tubing is brought to annealing temperature by electric current passed through a section of the tubing intermediate a pair of peripherally grooved contact wheels of substantnal diameter, and sparking is substantially eliminated by forming the tube contacting portion of at least one of the contact wheels of electrographitic material.

FIELD OF THE INVENTION The invention relates to continuous annealing or heat treatment of metal tubing such for example as relatively thin-walled copper tubing. The invention is not of course limited to copper but is applicable to tubing formed of copper alloys, aluminum or aluminum alloys, steel or the like.

In some cases the tubing may be supplied on a reel from which it is unwound and passed through the annealing equipment, after which it may be rewound on a reel. Alternatively of course, the tubing may comprise straight lengths which preferably are bent for more efficient wheel contact as it passes around a contact wheel but which is straightened after the annealing process is completed.

DESCRIPTION OF THE PRIOR ART Generally speaking, continuous annealing equipment has been provided for annealing wire or strip, but annealing equipment especially designed for treatment of metal tubing has not been available.

The problem of annealing tubing is quite different from annealing wire or rod for example, because of the difficulty in causing the tubing to bend smoothly and uniformly as it advances around a portion of a contacting wheel. Metal tubing tends to undergo local bending or kinking, leading to vibration or bouncing, which in turn leads to sparkling betweeen the contact wheel and the tubing. Particularly, in the case of thin-walled tubing, this sparking cannot be tolerated. In the first place, it leads to pitting and possible puncture of thin-walled tubing. Even if this does not occur, the sparking results in pitting both of the tubing and the wheel and as the pit on the wheel comes around into contact with the tubing there is a tendency for further sparking which aggravates the problem.

A further reason why equipment supplied for strand annealing of wire or rod is not suitable for tubing is that the tubing has a much lower tensile strength than wire having the same cross-sectional area of metal. Furthermore, bending of tubing produces temporary thickening at the inside of the bend and corresponding thinning of the tubing at the outside'of the bend. In addition, problem are encountered in introducting the necessary relatively heavy current flow into thin-walled tubing suflicient to produce the entire current density through the entire periphery of the tubing, without producing a sufliciently heavy current flow at the zone of contact to burn or otherwise damage the material of the tubing.

The only prior art patent which has been called to the attention of the inventors is Quarnstrom et al. 2,240,019. This patent discloses a particular form of Bundy tubing but makes the broad statement that it is applicable to other types such as tubing fashioned from a single strip having either single or double ply. The patent makes no disclosure of any structure capable of suppressing harmful sparking as the tubing advances between electrical contact wheels or rolls.

SUMMARY OF THE INVENTION In accordance with the present invention, electrically conducting metal tubing, preferably of relatively small size as for example between A" and 1" outside diameter, is continuously advanced between a pair of peripherally grooved electrical contact Wheels separated by a distance selected in accordance with the density of current flow so as to bring the intermediate length of tubing to the required annealing temperature during transit between the wheels. Associated with the electrical contact wheels are guide wheels positioned to cause the tubing to be bent as it passes around a portion of the periphery of the contacting wheels. It has been found that harmful sparking occurs most significantly at the exit contact wheel, and accordingly, at least this wheel, and if desired, both electrical contact wheels, are provided with grooved peripheral portions of spark or are suppressing material. Best results have been encountered when the peripheral grooved portion of the contact wheels is formed of electrographitic material.

It is accordingly an object of the present invention to provide annealing equipment for thin-walled metal tubing comprising a pair of peripherally grooved electrical contact wheels over which tubing is continuously advanced, and providing at least one of the Wheels with a peripheral grooved portion formed of spark supperssing material.

It is a further object of the present invention to provide annealing equipment as described in the foregoing in which at least the electrical contact wheel engaged by the heated tubing is provided with a grooved peripheral portion of electrographic spark suppressing material.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawing, illustrating a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic elevation view showing the annealing equipment.

FIG. 2 is an enlarged fragmentary sectional view on the line 2-2, FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT While equipment has long been available for the purpose of strand annealing of straight material such as wire or rod, or strip, this equipment has provided unsatisfactory for annealing relatively thin-walled metal tubing. Ill-accordance with the present invention the annealing equipment is provided in an arrangement illustrated more or less diagrammatically in FIG. 1. In this figure there are provided a plurality of peripherally grooved guide and contact wheels, the guide wheel being provided at the tube entering end of the equipment, and the guide wheel 12 being provided at the tube exiting end of the equipment. Electrical contact wheels 14 and 16 are provided to engage an intermediate portion of the tube T. All of the wheels are mounted in relatively thin sealed housings 18, 20, 22 and 24, and connecting tube 26, 28 and 30 are provided intermediate the housings to protect the tubing from oxidation. Preferably, a gas is introduced into the housing 24 in which the wheel 12 is located, and this gas may be deoxidizing natural gas or cracked gas. The gas is caused to flow successively through the housing 24, tube 30, housing 22, tube 28, housing 20, tube 26 into the housing 18 from which it exhausts. In addition, it is desirable to purge the inside of the tubing prior to bringing it to annealing temperature and this may be accomplished in any suitable manner by introducing a purging gas to one end of the tubing and blowing it through the tubing to expell all of the air from the interior.

The problem in annealing the tubing is of course to bring the tubing as it is continuously advanced, to the proper annealing temperature, after which the tubing is cooled or quenched as required, such for example as by passing it through a water bath or water spary. This is most conveniently accomplished during continuous advance of the tubing by causing the tubing to advance between a pair of electrical contact wheels 14 and 16 suitably connected into an electric circuit so that the portion of the tubing which is intermediate the wheels 14 and 16 forms a part of the circuit. Thus, the portion of the tubing intermediate the contact wheels is heated by electrical resistance heating as it advances so that as it leaves the exit contact wheel 16 it is at the required temperature for further processing.

It is desirable to provide the guide wheels 10 and 12 in such relationship to the contact wheels 14 and 16 so as to cause the tubing to be bent as it passes around the contact wheels so as to have extended electrical contact therewith. This not only reduces the current density to safe values, but also tends to eliminate to some extent the undesirable flutter, vibration or bouncing which occurs as the tubing engages the contact wheels.

However, even with the most advantageous arrangement of contact wheels and guide wheels, it has been found very diflicult to avoid harmful sparking between the tubing as it moves into and out of contact with the electrical contact wheels. This has been particularly noticeable at the exit contact wheel 16.

In accordance with the present invention, this harmful sparking, which previously produced burned areas on the tubing and also produced pitting of the tube and wheel, has been substantially completely eliminated by forming at least the exit wheel 16 in an arrangement best seen in FIG. 2.

As seen in this figure, the wheel 16 is carried by a shaft 32 which extends through an opening 34 in the housing 22. The opening is sealed by a suitable seal indicated generally at 36 which prevents escape of the deoxidizing gas circulated through the housing 22. The wheel assembly 16 comprises the wheel 38, which may be formed of cooper or aluminum, and is attached to a flange 40 on the shaft 32 by suitable means such as screws 42. At the periphery of the metal wheel 38 is an annular electrical contact ring 44 provided with a peripheral groove 46. The contact ring 44 is secured to a mounting ring 48 by screws 50, the mounting ring 48 in turn being attached to the wheel 38 by mounting screws 52.

The groove 46 in the contact ring 44 is preferably provided with straight side walls having an included angle of approximately 60 degrees and terminating in a circular fillet at the bottom having a radius somewhat less than 0.200. The material of the contact ring 44 is a spark suppressing material and excellent results having been obtained when the material is an electrographitic material of the type commonly used for electrical contact brushes. A suitable material for this ring is furnished by the General Electric Company under their grade designation of ME18 brush material and is described by the supplier as an electrographitic material of moderate hardness, the final product being of a fairly highly graphic nature. The material is described as having the following physical properties:

Density1.65 Hardness-50 Compressive strength6,500 p.s.i. Transverse strength--3,800 p.s.i. Modulus of elasticity p.s.i. 1O l.2 Temperature Limit:

Neutral at-mosphere-5000 F. Oxidizing atmo-sphere750 F. Coefficient of thermal expansion in./in./C 10 -3.0 Permeability ,uDarcys35,000 Max. grain size0.003"

One of the problems which is involved is relative slippage between the tubing an the peripheral portion of the electrical contact wheels due to the expansion of the tubing as it is brought to annealing temperature. Preferably, all of the wheels 10, 12, 14 and 16 are driven at uniform peripheral speed. The electrographitic peripheral portion of the electrical contact wheels apparently facilitates this slippage wtihout particular wear on the groove 46. Tests indicate that a contact ring 44 formed of the electrographitic material described 'will have a useful life of over one year, operated two shifts a day, or a life expectancy of two years if operated only a single shift a day.

Obviously, some wear occurs on the graphitic wheel and the depth of groove increases and the nature of contact varies. Initially, the contact between the sides of the wheel and the outer surface of the tubing is theoretically twoline contact extending along spaced portions of the tubing.

As the groove in the contact ring wears, the area of contact increases until eventually, the tubing has a single relatively large area of contact. However, the wheel operates efiiciently without producing serious sparking problems even prior to initial wear or break-in, and as indicated above, continues to operate with an extremely long life expectancy.

While the electrographitic material of the ring 44 has extremely good wearing properties in contact with the advancing tubing, the material is relatively brittle and it is desirable to support the ring by a support ring 54 which engages most of the outer area of the contact ring 44 and is retained in position by a multiplicity of mounting screws 56.

In order to dissipate heat from the structure, it is desirable to provide a water spray directed against the outer surface of the wheel 38 and a suitable nozzle for this purpose is indicated diagrammatically at 58. In order to prevent the water from this spray from reaching the groove 46 in the contact ring 44, the mounting screws 56 which attach the ring 54 to the wheel 38 also mount a dished guide plate 60 in the relationship illustrated in FIG. 2, which serves as a deflector for preventing water from flowing around the underside of the wheel into the contact groove 46.

While the electric current may be supplied to the contact ring 46 through the shaft 32 and the wheel 38, it is preferable to provide a shorter flow path by mounting brushes 62 within the housing 22 in contact with the mounting ring 48 and in close proximity to the contact ring 44. As illustrated in the figure, the brushes 62 are maintained in contact with the mounting ring 48 by compression springs 64 located in hollow mounting brackets 66. The electrical wiring 68 extends through an opening in the housing provided with a gas-tight seal 70.

The location of the brushes 62 is indicated in FIG. 1, and in order to balance the slight thrust of the brushes imparted by the compression spring 64, rollers 72 are provided to engage the surfaces of the mounting ring 48 diametrically opposite to the portions thereof engaged by the brushes 62.

What we claim as our invention is:

1 In tube annealing equipment, a pair of peripherally grooved electrical contact wheels, a pair of guide rolls positioned to cause advancing tubing to be bent around both of the contact wheels through a substantial arc, means for connecting an electric circuit to the contact wheels so as to require current to flow through the portion of tubing intermediate the contact wheels, means for advancing the tubing continuously and rotating the wheels, the peripheral portion of at least one of the electrical contact wheels being formed of electrographitic spark suppressing material.

2. Apparatus as defined in claim 1 in which said electrographitic material is carbon brush material.

3. Apparatus as defined in claim 1 in which the groove in the periphery of the wheel is initially formed with side walls which are straight in radial cross-section and which converge to provide an included angle of approximately degrees.

References Cited UNITED STATES PATENTS 4/1941 Quarnstrom et al. l48-12.3 8/1968 McFarlane 219-- 

